Great cast, but season 2 really sucked. They took the goodwill earned with season 1 and just mangled it. There is some redemption in season 3. Olivia Colman did so well that they passed a law to put her in every single British drama and comedy from now on. And she keeps killing it! (see Fleabag)
Much like Bloodline, series 1 is phenomenal, series 2, not so much, and series 3 is a return to form. That said, I really enjoyed this show. It's like Twin Peaks, but without all the surreal, David Lynch stuff.
The altercations between Colman and Tennant are great, the characters are OK and their stories engaging if rather disjunct, but all the rest is misery. The premise is very clear: an outsider detective finds his way into a small town communal dirt and keeps digging. But the way he deals with the actual crime story is an absolute disgrace for the viewer, who is taken for stupid.